The files of WordPress define many useful PHP functions. Some of the functions, known as Template Tags, are defined especially for use in WordPress Themes. There are also some functions related to actions and filters (the Plugin API), which are therefore used primarily for developing Plugins. The rest are used to create the core WordPress functionality.

Many of the core WordPress functions are useful to Plugin and Theme developers. So, this article lists most of the core functions, excluding Template Tags. At the bottom of the page, there is a section listing other resources for finding information about WordPress functions. In addition to this information, the WordPress phpdoc site details all the WordPress functions by version since 2.6.1.

You can help make this page more complete!

Here are some things you can do to help:

Add documentation to un-documented functions, by creating sub-pages or at least by adding short comments in the lists below. If you create a subpage for a function, please include information and examples of usage of that function, if possible, per the examples found in Template Tags.

List more functions here, following the category structure.

Correct errors by moving functions to better categories where appropriate, and of course fixing typos. Note: that it is OK for a function to appear in more than one category.

WordPress Variable Report - A list of WordPress functions, listing what version of PHP every function requires (and if there's a compatible function available), what varables/arguments in functions are unused, and what functions/variables each class contains (and their default values).

WordPress Hooks Table - A list of WordPress actions and filters, cross-referenced to the files they are in